Fix a long-standing spec compliance bug where Synapse would accept a trailing slash on the end of `/get_missing_events` federation requests. (#13789)

* Don't accept a trailing slash on the end of /get_missing_events

* Newsfile

Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>

Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>

changelog.d/13789.bugfix

@@ -0,0 +1 @@
+Fix a long-standing spec compliance bug where Synapse would accept a trailing slash on the end of `/get_missing_events` federation requests.

synapse/federation/transport/server/federation.py

@@ -549,8 +549,7 @@ class FederationClientKeysClaimServlet(BaseFederationServerServlet):
 
 
 class FederationGetMissingEventsServlet(BaseFederationServerServlet):
-    # TODO(paul): Why does this path alone end with "/?" optional?
-    PATH = "/get_missing_events/(?P<room_id>[^/]*)/?"
+    PATH = "/get_missing_events/(?P<room_id>[^/]*)"
 
     async def on_POST(
         self,